I run two group 31 Duracells for my 80lb Terrova. I'm getting about 8 hours of trolling crank baits at 1.7 mph on an 18 foot Alumacraft. I had two group 27 Interstates but couldn't get 6 hours of run time pulling harnesses with them.
What everyone fails to realize is that there are only a couple different battery manufactures out there.
AGMs are great if you're running in very rough water. They take the shock really well in big water. You won't get longer run times by going to an AGM. I've used many different brands and types of batteries. I tournament fish and know a bunch of others that pound the water multiple times a week. The most popular batteries that I've heard of guys running are the Wal-Mart brand deep cycles, Duracells, Fleet Farm brand, and the Cabelas brand. If a guy looks up the makers of all the different brands you'll see that the only difference is usually the case the battery comes in. Internally, unless buying AGM or lithium they are all the same.
Like what was said before, look at the reserve capacity at 25 amps. Buy the longest reserve capacity and heaviest battery in the size you want. A 56 lb 31 series will not last as long as a 64 lb 31 series. There is more lead and acid. It can be there simple. Also, look at the manufacture date and buy the newest possible even if that means pulling 15 off the shelf to find the newest ones in the back.
I have a Minn Kota 3 bank, 5 amp onboard charger on my boat that is about 3-4 years old (I don't have the specific model right now).
If I were to get new AGM batteries, can I charger them with my on board charger or is the chager programmed from lead acid batteries? I will have to look when I home, but I don't believe there are any buttoms to adjust for the type of battery.
I don't want to ruin 2 brand new batteries with the wrong charger.
Hehe, if you want intimidating high cost, go Iron Phosphate. I did. After the heart settles down from the sticker shock, the pros far out weigh the price. This will be my forth year with them and they rum like day one.
Oh, and just over 20 lbs each. They are light as a feather compared to wet cell. I can mount them on their side, or upside down if I wanted to. And charge time is so short, that if I forget to plug them in and catch it that morning, they charge in the time it takes to cook and eat breakfast.
I'll never go back to lead.
I ended up getting two "Duracell Ultra AGM Group 31's".
I believe they are $240 a piece, but you can save 10% if you order online and pick up in store and there is also a $10 mail in rebate for each battery.
Hard to pass that up.
https://www.batteriesplus.com/battery/marine-and-boat/deep-cycle/bci-group-31m/sli31dtmagmdc
Maybe even 15% off now.
Edit: Sumbitches are heavy, like 67lbs a piece.
I couldn’t agree more with musky. The perverbial nail on the head. I had nothing but gassing issues with wet cells. Ruined carpet, floor, etc. I went with 12v cuz to be honest I didn’t know any better an totally regret it. I opted for 3 road runner AGM and couldn’t be happier. No gassing, no wet cell issues at all. In my opinion AGM is the ticket. Whatever you get, by far AGM is better. The initial cost is by far higher and intimating and costly. No disputing that. However, for me the damage and unknown was the factor. AGM s are better in the long run. I feel hold charge better and longer. As well as charging characteristics. Long story short.... if affordable then get them. If a 12 vs 24 is another issue, get a 24. Wish I did. It’s only an opinion but I hope the best for your decision. I get it. The cost sucks. $180-200+ Ea is absolutely hard to justify. Took me a long time to decide what to do but I’m 100% Glad I did get the AGM. Oh it’s the road runner from fleet, but I guess any AGM is great.
If you didn't want to run two at the same time I would just hook both batteries to a switch when the one gets low just flip the switch no messing around with connections. Plus its beneficial to have a switch to turn off power to the trolling motor if you don't unplug it.
Id just bring two with ya. I always did. Then when one is done hook up the other. Its not like you have more power, just double the capacity. I haven't done it but im not sure you will be gaining anything other than not having to hook up your other battery later. I wouldn't be too concerned unless you are in a tournament or just planned a trip where you will be on the water all day pulling yourself around. In that case, its best to have 2. It sucks to not be able to fish effectively because of a dead battery. Been there before, its horrible
I'd never buy an Optima, I had horrible luck with them.
Regular Deep cycle are ok if you don't fish a lot and want to be disappointed at 4pm when your battery is toast. 
. Although to be honest, I think anyone running a 12v trolling motor, no battery will last you all day if you using it a lot.
AGM - cabela's advanced angler are what i have. Going on 8 years now, I keep them plugged in all winter. If you fish all day and on the motor hard, AGM's are the way to go IMO.
Deep cycle batteries are NOT supposed to be discharged past 25%, you'll ruin them fast. I know, I used to beat them on the Mississppi till they were drained and it didn't matter what brand. I used to go through 2 big DC batteries before dark. I killed the Optima's with my 12v too.
I decided to stop playing around and bought a 24v with AGM's. I can beat the snot out of it and I don't believe i ever took it past half.
Just my take on the matter.
